1) Field of the Invention
The present invention relates to a control unit for an electric power steering apparatus for use in a vehicle which accomplishes the reduction of driver's steering effort and the improvement of steering feelings.
2) Description of the Related Art
In an electric power steering apparatus, a rotating direction or rotational torque of an electric motor is controlled in accordance with an assist signal calculated on the basis of an output signal of a torsional torque sensor made to detect a torsional torque in a steering system, thereby reducing a steering load imposed on a vehicle driver. For example, for a high-response electric power steering apparatus, there has been proposed a technique in which, for generating a rotational torque needed, an actual motor current to be detected through the use of a motor current detecting circuit is controlled to reach a predetermined current value (for example, Japanese Patent Laid-Open No. 2000-238652).
However, the motor current detecting circuit shows a characteristic in which its output varies with temperature stemming from the temperature characteristic of an operational amplifier. Accordingly, there is a problem in which, if an electric motor is controlled on the basis of an output of such a motor current detecting circuit, the steering torque varies in accordance with a variation of temperature. In particular, in recent years, since the gain of the current detecting circuit has been higher than before, a minute variation of a current detection output stemming from a temperature variation can exert adverse influence on driver's steering feelings.